Sounds like you are in my area. Beans about a foot tall. Beans are ready but plant is not. Have a F2 with Ausherman bars and new concaves and we had to set them down to 1_4" to thrash the pods. Start with this setting and adjust your cylinder speed accordingly. It has been my experience that speed is the biggest culprit to cracking beans, not cylinder clearance. Open top sieve just enough to let any unthrashed pods through and bottom sieve open just enough to let beans drop through. Watch your return elevator, it will tell you what you need to do.